This invention relates, in general, to hydraulic gear pumps and motors and especially to gear pumps and motors operable at sustained high pressures.
Hydraulic gear pumps or motors are well-known fluid machines. Such machines generally consist of a central housing with a gear pocket, an end cover, and an adapter cover. A pair of meshed gears are rotatably mounted inside the housing. The gears may be keyed to, or integral with, their gear shafts which are rotatably supported by bearings located in the covers of the machine. One gear shaft extends through the adapter cover for connection to a drive shaft. In the case of a pump, fluid enters the machine through a low pressure inlet adjacent to a point where the volume between the gears is increasing. The fluid is then carried between the teeth of the gears around the outer periphery of the gear pocket to a point where the gears begin to mesh and the volume between the gears is decreasing. There fluid is forcibly discharged through a high pressure outlet.
The longevity of a gear-type hydraulic machine depends upon a number of factors, including the alignment of the gears with each other, the gear-to-housing contact, the load on the bearings and the operating pressure. Those skilled in the art will recognize that the higher the operating pressure, the more detrimental are the effects of misalignment, excessive housing contact, and bearing load. Others have attempted to compensate for the deleterious effects of sustained high pressure operation by providing fluid machines having heavier housings or covers, high precision machining of the components, sealing off the bearings from the high fluid pressures, and by providing one-piece wear plate and bushing supports which are in turn supported in the end and adapter covers.
Examples of the latter type of combination wear plate and support member are found in U.S. Pat. Nos. 3,421,769 and 2,714,856. In order for a single structural member to accommodate all of the loads created by the high pressure forces, it is necessary that the wear plate be precisely machined and that the housing and the end covers be relatively massive and thick-walled to accommodate all of the loads. Accordingly, such machines are difficult to produce and are also expensive due to the precision machining and extra material that are shown in U.S. Pat. No. 3,063,378. There, a wear plate is used to maintain the alignment of the gears. Spaced on the wear plate are two pairs of cooperating split spacer rings which fit around each of the four bearings that support the gear shafts. However, the split spacer rings do not prevent high pressure fluid from entering the bearings and there is no provision for replenishing or exchanging the fluid in the drive shaft bearings.